Production of 1,4-naphthoquinone

ABSTRACT

Naphthalene in carbon tetrachloride has been oxidized by chromic acid to 1,4-naphthoquinone, the reaction being controlled by gradual addition of the sulfuric acid to the otherwise complete naphthalene-sodium dichromate-water-carbon tetrachloride reaction mixture. The yield of naphthoquinone has now been increased to about 60 percent, based on the naphthalene charge, by maintaining the weight ratio of carbon tetrachloride to naphthalene at a level within the range of 0.3:1 to 3:1.

United States Patent J00 et al.

[451 Aug. 1,1972

[ 1 PRODUCTION OF 1,4-

NAPHTHOQUINONE [72] Inventors: Look A. Joo, Johnson City; Loren A.Bryan, Elizabethton, both of Tenn.

[73] Assignee: Great Lakes Carbon Corporation,

New York, NY.

[22] Filed: Dec. 22, 1966 [21] Appl. No.: 603,730

[52] US. Cl. ..260/396 R [51 Int. Cl ..C07c 49/66 [58] Field of Search..260/396, 396 R 56] References Cited UNITED STATES PATENTS 2,402,2266/l946 Hyman etal ..260/396 Primary Exarniner-lnrraine A. WeinbergerAssistant Examiner-L. Arnold Thaxton Attorney-Armand McMillan ABSTRACTNaphthalene in carbon tetrachloride has been oxidized by chromic acid to1,4-naphthoquinone, the reaction being controlled by gradual addition ofthe sulfuric acid to the otherwise complete naphthalenesodiumdichromate-water-carbon tetrachloride reaction mixture. The yield ofnaphthoquinone has now been increased to about 60 percent, based on thenaphthalene charge, by maintaining the weight ratio of carbontetrachloride to naphthalene at a level within the range of 0.321 to3:l.

2 China, No Drawings PRODUCTION OF 1,4-NAPHTHOQUINONE This inventionrelates to an improvement in the method for oxidation of naphthalene tonaphthoquinone in the presence of an organic solvent. More particularly,it relates to an improved method for the manufacture of naphthoquinoneby direct oxidation of naphthalene with hexavalent chromium at anincreased yield.

REVIEW OF PRIOR ART There are many processes outstanding in the art forthe production of naphthoquinone, an important compound with fungicidalproperties that has been widely used as an intermediate in the synthesisof dyes and fungicidal derivatives well accepted in agriculture and inthe textile industry.

Some of the methods which have been used in the past involve the vaporphase oxidation of naphthalene with air over a stabilized vanadium oxidecatalyst. The usefulness of the vapor phase oxidation method has beendiscounted severely by the difficulties experienced in obtaining goodquinone from the oxidate mixtures, contaminated as they are with, amongother things, 10 percent to 40 percent of unconverted originalnaphthalene. Another type of approach to naphthoquinone which is stillin current use calls for the condensation of benzoquinone withbutadiene. The shortcomings of such a process in number of chemicalsteps, time consumption and apparatus requirement anhydride or sodiumdichromate and acetic acid or a mineral acid such as sulfuric acid. Mostof these methods are slow, yield relatively low quantities of thequinone and favor the production of phthalic acid.

One of the methods however, that of Hyman and Peters described in US.Pat. No. 2,402,226, involves the innovation of adding to the chromicacid system (Na,Cr,OB7=H,SO,), 5 to volumes, based on the naphthalene,of an inert immiscible solvent such as carbon tetrachloride. Thesolvent, acting as a vehicle or carrier for the naphthalene, provides asecond phase 50 which overlays the solution of oxidizing agent. By goodagitation and control of the reaction temperature through selection of asolvent with the appropriate reflux temperature, yields ofnaphthoquinone of about 40 percent are achieved. When a beta-substitutednaphthalene is oxidized under these conditions, strikingly better yieldsof the corresponding quinones are obtained, e.g. percent to percent inthe case of the monomethyl compound and nearly quantitative yields forthe dimethyl isomers.

OBJECTS OF INVENTION It is an object of this invention to maximize theyield of a-naphthoquinone in the direct oxidation of 65 naphthalene withhexavalent chromium.

Another object is to increase the conversion of naphthalene to the pointwhere the unconverted startoxidation of 5 ing material does notsignificantly handicap the recovery of good quality naphthoquinone.Another object is to aflect the ratio of naphthoquinone to phthalic acidin such a manner that the production of naphthoquinone is stronglyfavored. Still another object is to effect economies in equipment andreagents to an extent that the process of the invention can seriouslychallenge current production methods such as the benzoquinone-butadienecondensation.

SUMMARY OF INVENTION These and other objects which shall become apparentin the course of the ensuing disclosure, have been accomplished bydrastically altering the weight ratio of solvent to naphthalene employedin the chromium compound oxidation process to a level within the rangeof from about 0.3:l to about 3:1. This change in reaction conditions hasresulted in the obtention of an average naphthalene conversion of about90 percent, an average yield of a-naphthoquinone of about 58 i 2 percentand an average naphthoquinone to phthalic acid yield ratio of 2.260.10:1. That such possibilities lay hidden in departing from the processas specified by Hyman and Peters was unpredictable in view of the factthat it had been established that the better yields of quinone wereobtained at the higher dilution volumes. To obtain therefore an averageincrease in yield of close to 50 percent by weight by reducing theminimum recommended ratio to the maximum which is less than half of theformer while not encountering the difficulties which originally led tothe use of a diluent is, to say the least, surprising. No lesssurprising is the fact that when other solvents are used, such asbenzene, which have been proposed as equivalents of carbontetrachloride, neither the maximization of the yield nor the improvementof the naphthoquinone to phthalic acid ratio is achieved by a reductionof solvent concentration of the magnitude recommended by the presentinvention.

DETAILED DESCRIPTION The following examples and procedures willillustrate the invention in executional detail. These examples are notto be construed however as limitations of the invention other than thoseembodied in the appended claims. All parts and percentages given in theillustrations shall be on a weight basis unless otherwise noted.

Oxidation Procedure No. 1

Sodium dichromate dihydrate, 366 parts, is dissolved in 50 C water, 136parts, and the resulting solution is placed in the reaction vessel alongwith carbon tetrachloride, I26 parts, and naphthalene, 90 parts. Thisgives a solvent to naphthalene ratio of 1.4:] or, on a volume basis,lzl. Only part of the naphthalene dissolves under these conditions. Thereaction vessel is equipped with means to reflux, distill, stir, cooland heat. With vigorous stirring of the content of the vessel, there isthen added dilute sulfuric acid, 534 parts percent sulfuric acid inparts water, at a rate consistent with maintenance of a temperature ofabout 40 C or less in the reaction mixture. The addition takes from 60to 90 minutes. Once it is completed, the reac tion mixture is warmed toabout 60 C and is maintained at that temperature for about 90 minutes.The

stirring is continuous. At the end of this period, the heating rate isincreased and the carbon tetrachloride distills off between 66 and 90 C.After the distillation has been completed, the residue is cooled to atempera ture below 50 C by dilution with cold water or ice and thematerial is filtered. The cake is washed until free of chromium saltsand dried in a forced draft oven at 80 C. The naphthoquinone is thenseparated from the byproduct phthalic acid and from residual naphthaleneby conventional methods or modifications thereof.

The effect of varying the ratio of solvent to naphthalene inpreparations made according to the oxidation method No. l are given inTable 1.

( l Based on weight charged; the purity (assay) was 89% C,,,l-l, (2)Based on naphthalene in the charge (3) Based on naphthalene disappearingin the reaction An examination of the data in Table 1 reveals asignificant increase in the yield of naphthoquinone when naphthalene isoxidized in a solvent-poor medium. It is indeed remarkable that such animprovement is obtained at solvent to substrate ratios which have beenadjusted in a direction opposed to the teachings of the prior art and tolevels beyond those which have previously been employed.

Oxidation Procedure No. 2

A second method which illustrates the invention is carried out inapparatus that is the same as that used for Procedure No. 1, except thatthe volume of the reactor is reduced by one-half. This procedure differsfrom the first one in that the chromic acid necessary to oxidize thenaphthalene. is formed before addition to the naphthalene slurry, whilein Procedure No. 1, it is formed in situ, as needed, by the gradualaddition of sulfuric acid to the otherwise complete reaction mix ture.The latter technique is more desirable, as shown by the results.

Sodium dichromate dihydrate, 184 parts, is dissolved in water, 206parts, and to the resulting solution is gradually added 268 parts of 95percent sulfuric acid. The reactor in turn is charged with naphthalene,45 parts, and carbon tetrachloride, 63 parts. This corresponds to asolvent to naphthoquinone weight ratio of 1.4:] or volume ratio of 1:1.With vigorous stirring of the reactor contents, the chromium solution isadded over a period of two hours while the temperature of the reactantsis maintained at about 40 C or less. The stirring is continued for 30 to45 minutes after the addition of the oxidant is completed. The reactionmixture is then heated with continual stirring until its temperature hasreached 90 C. After the distillation of the carbon tetrachloride hasterminated, the residue in the reactor is poured into cold water or overcracked ice, 200 to 300 parts. When the mixture has cooled to about roomtemperature, it is filtered. The cake is washed free of chromium saltsand dried in a forced draft oven for one to two hours. The product maythen be recovered according to conventional or other methods.

Variations of solvent to naphthalene ratio within the limits shown inExamples 6, 7 and 8 have given the results tabulated below when carriedout as part of Procedure No. 2.

TABLE 2 Yield 11" Apparent Naph- CCI l ,4- Phtthalene C H NaphthohalicConversion Example Weight quinone Acid '1:

( I Based on weight of charge; purity (assay) 95.5% C H. (2) Based onnaphthalene charged (3) Based on naphthalene disappearing in thereaction Again the yield and conversion of naphthalene is highest at asolvent to naphthalene ratio of 1.4: 1.

It thus becomes evident that the selection of the preferred ratio ofsolvent to naphthalene permits greater efficiency to be obtained throughmaximum conversion and highest yield for the given system under a fixedset of conditions. With carbon tetrachloride this preferred ratio lieswithin the range of about 0.321 to 3:] on a weight basis, whichcorresponds to a volume ratio range of approximately 0.2:1 to 2.2: l.

The nature of the reaction of instant interest as well as the conditionsunder which it is performed narrow considerably the choice of usablesolvents. These must be organic liquids capable of dissolvingnaphthalene and cur-naphthoquinone to some extent. They must beimmiscible with water and of course fairly resistant to chrornic acidoxidation. Temperature requirements for reaction and recovery furtherlimit the choice to liquids having a boiling point not greater thanabout [00 C. Thus, while it is conceivable that some degree ofimprovement in naphthoquinone production could be obtained by theexercise of this invention with solvents that do not meet all thesestringent requirements, it has been found that the best yields ofnaphthoquinone with the least net consumption of solvent, reactants andenergy, have been obtained with carbon tetrachloride used at a ratio tonaphthoquinone of about l.4:l on a weight basis, or about 1:] on avolume basis.

What is claimed is:

1. In the process of oxidizing naphthalene to alphanaphthoquinone bysubjecting naphthalene in the presence of carbon tetrachloride to theaction of an oxidant consisting essentially of an aqueous solution of ahexavalent chromium compound and a mineral acid while intensivelyagitating the reaction mixture, the improvement comprising limiting theweight ratio of carbon tetrachloride to naphthalene to the range of0.3:l to 3:1 and maintaining the reaction mixture at a temperature notgreater than about 40 C at least until the completion of the addition ofsaid oxidant.

2. The process of claim 1 wherein the carbon tetrachloride tonaphthalene ratio is about 1.4:] on a weight basis.

2. The process of claim 1 wherein the carbon tetrachloride tonaphthalene ratio is about 1.4:1 on a weight basis.